The present invention relates to a fabric web having a high modulus of elasticity used as a spring element in an upholstered article such as a seat or a bed, for example, and more particularly to a joint structure for joining such a fabric web to a metal rod serving as a frame member of such an upholstered article.
FIG. 1 of the accompanying drawings illustrates, partly cut away, a conventional upholstered seat comprising a seat frame 01 supporting a plurality of zigzag metallic springs 02 between opposite frame members thereof. The upholstered seat also includes padded cushioning members 03 placed on the springs 02 and each covered with a cover layer 04.
Another known upholstered seat, shown in FIG. 2, has a seat frame 05, a plurality of parallel fabric webs 06 of a high modulus of elasticity, woven of polyester yarns, and padded cushioning members 07 placed on the fabric webs 06 and each covered with a cover layer 08. The upholstered seat of FIG. 2 is lighter than the seat of FIG. 1 because no metallic springs are employed in the seat.
FIG. 3 shows still another upholstered seat of a conventional design. The upholstered seat of FIG. 3 is similar to the seat of FIG. 2 except that wider fabric webs 09 are supported by a plurality of wires 010 on the seat frame 05.
In each of the upholstered seats illustrated in FIGS. 2 and 3, each end of each of the fabric webs 06, 09 is folded on itself over a metal rod 011 (shown in FIGS. 3 and 4) which is fastened to the wires 010 or which is a member of the seat frame 05 (FIG. 2). A heat-fusible resin film 012 (FIG. 4) is interposed between the folded end and the unfolded body of the fabric web, and then focused by the high-frequency heating process to join the folded end and the unfolded body of the fabric web. The fabric web is thus fastened to the metal rod 011.
The above known joint structure is however disadvantageous as follows: If the metal rod is not subject to surface treatment, rust tends to be produced on the surface of the metal rod. While the upholstered seat is in repeated use, the fiber surfaces of the fabric webs 06, 09 are abraded by the rust layer, and rust particles are caused to enter between the fibers of the fabric webs, with the result that the fabric webs 06, 09 will be reduced in durability.
As shown in FIGS. 4 and 5, the fabric web is typically woven of weft yarns 013 extending in the direction of the arrow A in which the fabric web is kept under tension and warp yarns 014 which alternately overlie and underlie the weft yarns 013 perpendicularly thereto. Generally, the warp yarns 014 are made of nonelastic fibers such as polyester fibers and the weft yarns 013 are made of highly elastic fibers such as polyester elastomer fibers that are much more elastic than the warp yarns 14. When the fabric web 06, 09 is tensioned in the direction of the arrow A such as by the user sitting on the upholstered seat, the fabric web is stressed mainly at opposite marginal edges of a fused transverse area B near the metal rod 011. During repeated application of the stress to the marginal edges of the area B, the weft yarns 013 in the marginal edges are liable to unravel off the warp yarns 014, allowing the marginal edges to be disintegrated. Accordingly, the fabric web 06, 09 has a low degree of durability.
Another problem is that when the fabric web 06, 09 is tensioned, the weft yarns 013 are stretched and so is the heat-fusible resin film 012 which bears the stress applied to the area B of the fabric web. If the tensile strength of the heat-fusible resin film 012 were not high enough, it would be torn apart thereby to force the fabric web off the metal rod 011. The upholstered seat would thus be less durable.